1. Field of the Invention
The present invention relates to a mirror device for a single lens reflex camera.
2. Description of the Related Art
FIGS. 1A and 1B are center section views of a conventional single lens reflex camera with the photographic lens removed. In general, the mirror device of a single lens reflex camera is moved as indicated in FIGS. 1A and 1B in accordance with the operating state.
The mirror arrangement shown in FIG. 1A pertains to the state in preparation for optical exposure. A main mirror 10 directs the optical path of the photographic frame to a pentagonal prism 2 to allow the photographer to view the photographic frame through a finder 3. At the same time, the luminous flux of the rangefinder area passes through the half mirror part of the main mirror 10, and is directed to a rangefinder unit 4 via a sub-mirror 20. Rangefinding calculations are executed based on the output of the rangefinding unit 4.
On the other hand, the mirror disposition during optical exposure is shown in FIG. 1B. When the main mirror 10 and the sub-mirror 20 are rotated upward to the retracted state outside the photographic optical path, exposure control is executed by a shutter 5, so as to optically expose the photographic frame on a film 6. At this time, the main mirror 10 is retracted to the pentagonal prism 2 side, and the sub-mirror 20 is retracted to a position covering the half-mirror area corresponding to the rangefinder area of the main mirror 10, so as to prevent inverse incidence of light from the finder 3 into the optical exposure path.
The main mirror 10 and the sub-mirror 20 rotate via the operation illustrated in FIG. 2. That is, a mirror holder 12 which supports the main mirror 10 is itself supported on a support shaft 8 so as to be rotatable relative to a mirror box, and move in rotation between the exposure preparation position A and the exposure position B indicated by arrow 92. A sub-mirror holder 22 which supports the sub-mirror 20 is itself supported by a hinge 14 so as to be rotatable relative to the main mirror holder 12, and move between the exposure preparation position A and the exposure position B via the hinge 14 together with the main mirror holder 12, and rotates about the hinge 14 to the main mirror holder 12 side at the exposure position B.
A mirror drive mechanism such as, for example, the mechanism shown in FIGS. 3A and 3B is provided at the side of the mirror box to operate the main mirror 10 in the aforesaid manner.
When the main mirror 10 is set at the exposure preparation position, i.e., when the mirror is in the down position show in FIG. 3A, an overcharge spring 34 supported on a mirror drive lever 33 presses down on the drive portion 16 of the main mirror holder 12, such that a force is exerted on the main mirror holder 12 in the mirror down direction (counter clockwise direction in the drawing) until the main mirror holder 12 is stopped by a stopper not shown in the drawing so as to be maintained in the exposure preparation position. Although the mirror drive lever 33 pivots about a support shaft 33s in the mirror up direction via a mirror drive spring 35, this pivoting is regulated by a mirror charge lever 36.
When the main mirror 10 is set at the exposure position, i.e., set in the up position, shown in FIG. 3B, the mirror charge lever 36 is released and moved downward, and the mirror drive lever 33 is rotated in a counterclockwise direction in the drawing via a mirror drive spring 35. At this time, the contact portion 33a of the mirror drive lever 33 presses upward on the drive portion 16 of the main mirror holder 12 so as to lift the mirror.
A mirror drive mechanism such as that shown in FIGS. 4A and 4B is provided to drive the sub-mirror 20.
When the set at the exposure preparation position, i.e., when set in the mirror down position shown in FIG. 4A, a sub-mirror holder 22 supporting the sub-mirror 20 is rotated about a hinge 14 which functions as a rotating shaft relative to the main mirror holder 12, such that the sub-mirror holder 22 is positioned so as to be open relative to the main mirror holder 12. One end of a sub-mirror drive spring 15 is attached to connector 22a of the sub-mirror holder 22, and the other end is attached to a connector 12a of the main mirror holder 12. The movement of the sub-mirror holder 22 is regulated a guide shaft 9 fixedly attached to the mirror box. The sub-mirror drive spring 15 exerts a force on the sub-mirror 20 in a counterclockwise direction in the drawing, until the sub-mirror holder 22 is stopped by a stopper not shown in the illustration.
When the sub-mirror 20 is set at the exposure position, i.e., set in the mirror up position as shown in FIG. 4B, the sub-mirror holder 22 is guided by the guide shaft 9 of the mirror box to the position shown in the drawing. The sub-mirror drive spring 15 exerts a force on the sub-mirror 20 in a clockwise direction in the drawing, so as to be folded outside the photographic optical path together with the main mirror holder 12.
As shown in FIG. 6, the respective exposure preparation positions of the main mirror 10 and the sub-mirror 20 are adjustable via the stoppers 18 and 28 provided in the mirror box. That is, a main mirror stopper 18 contacts the main mirror holder 12 which supports the main mirror 10. The main mirror stopper 18 is an eccentric pin, which allows adjustment of the stopper position, i.e., the rotation angle, of the main mirror holder 12 by rotating the main mirror stopper 18. A sub-mirror stopper 28 contacts the sub-mirror holder 22 which supports the sub-mirror 20, and this stopper 28 is also an eccentric pin which allows adjustment in the same manner as described above.
In mirror devices of the aforesaid conventional construction, when the main mirror holder 12 is moved via adjustment by the main mirror stopper 18, the angle of the sub-mirror also changes simultaneously therewith due to the movement of the hinge 14 functioning as the rotational axis of the sub-mirror holder 22 provided on the main mirror holder 12. Furthermore, since the sub-mirror 20 is maintained relative to the mirror box by sub-mirror holder 22 through the main mirror holder 12, there is a wide variation in the position of the sub-mirror 20 due to cumulative component errors. For this reason a complex adjustment mechanism is required to obtain the necessary positional adjustment operation for the sub-mirror 20. Furthermore, after the position has been adjusted, the position (3-axis) of the rangefinding unit 4 must be adjusted, as indicated by arrows 90 and 91 in FIG. 1A.